Two-stroke lubricating oils

ABSTRACT

The smoke index of a two-stroke engine is improved by utilizing as the engine lubricant a two-stroke engine oil that comprises a major amount of a GTL base oil.

FIELD OF THE INVENTION

This application claims the benefit of U.S. Provisional application 60/728,850 filed Oct. 21, 2005.

This invention relates to a lubricant composition useful as a two-stroke engine lubricating oil. More particularly, this invention relates to a two-stroke lubricating oil characterized by its reduced smoke generation characteristics.

BACKGROUND OF THE INVENTION

Two-stroke gasoline engines have found widespread use in a wide variety of garden and recreational equipment. For example, two-stroke engines are used in lawn mowers, chain saws, string trimmers, mopeds, snowmobiles and outboard marine motors to mention a few.

Two-stroke gasoline engines are operated using a mixture of gasoline and a lubricant in prescribed proportions.

Two-stroke engine lubricants are typically formulated with a lubricating mineral oil or synthetic base oil, a variety of additives to enhance performance characteristics and a solvent to enhance the miscibility of the lubricant with gasoline.

Hydrocarbon emissions from two-stroke engines, by virtue of their basic design, tend to exceed emissions from a comparable four-cycle engine. Moreover, the technological advancements for reducing emission from four-cycle engines have not been successfully adapted to two-stroke engines. Hence, there is a growing concern about emissions, such as visible smoke, produced by two-stroke gasoline engines.

Few smoke-reducing additives are commercially available to formulators of two-stroke lubricants. Some, like those that contain metals, are environmentally undesirable; and others, like polyisobutylenes, contribute to s exhaust port deposits and clogging which results in scuffing and power loss. Synthetic basestocks are known to reduce smoke in two-stroke engines, but they are cost ineffective.

Thus there is a need for a two-stroke gasoline engine lubricant composition that meets standard performance criteria, is cost effective and has good smoke emission characteristics.

SUMMARY OF THE INVENTION

Basically, the present invention is predicated on the discovery that a two-stroke engine oil that comprises a major amount of a GTL base oil has a smoke index greater than about 75.

Accordingly, one embodiment of the invention is a two-stroke engine oil composition comprising a major amount of a GTL lubricating base oil and an effective amount of at least one additive selected from the group consisting of extreme pressure additives, anti-foaming agents, pour point depressants, rust inhibition, antioxidants, detergents, dispersants and hydrocarbon solvents.

Another embodiment of the invention is a method for reducing observable smoke emitted from a two-stroke gasoline engine by using a lubricant comprising a GTL base oil.

These and other embodiments will become apparent from the detailed description that follows.

DETAILED DESCRIPTION OF THE INVENTION

The GTL base oils according to the invention are materials of lubricating viscosity that are generally derived from hydrocarbons, for example, waxy synthesized hydrocarbons, that are themselves derived from simpler gaseous carbon-containing compounds, hydrogen-containing compounds and/or elements as feedstocks. GTL base stocks and base oils include wax isomerates, comprising, for example, hydroisomerized or isodewaxed synthesized waxy hydro-carbons, hydroisomerized or isodewaxed Fischer-Tropsch (F-T) material (i.e., hydrocarbons, waxy hydrocarbons, waxes and analogous oxygenates), preferably hydroisomerized or isodewaxed F-T waxy hydrocarbons, or hydroisomerized or isodewaxed synthesized waxes, or mixtures thereof.

GTL base stocks and base oils derived from GTL materials, especially hydroisomerized/isodewaxed F-T material derived base stocks and base oils are characterized typically as having kinematic viscosities at 100° C. of from about 2 cSt to about 50 cSt, preferably from about 3 cSt to about 30 cSt, more preferably from about 3.5 cSt to about 25 cSt, as exemplified by a GTL base stock derived by the isodewaxing of F-T wax, which has a kinematic viscosity of about 4 cSt at 100° C. and a viscosity index of about 130 or greater. Reference herein to kinematic viscosity refers to a measurement made by ASTM method D445.

GTL base stocks and base oils derived from GTL materials, especially hydroisomerized/isodewaxed F-T material derived base stocks and base oils are further characterized typically as having pour points of about −5° C. or lower, preferably about −10° C. or lower, more preferably about −15° C. or lower, still more preferably about −20° C. or lower, and under some conditions may have advantageous pour points of about −25° C. or lower, with useful pour points of about −30° C. to about −40° C. or lower. References herein to pour point refer to measurement made by ASTM D97 and similar automated versions.

The GTL base stocks and base oils derived from GTL materials, especially hydroisomerized/isodewaxed F-T material derived base stocks and base oils are also characterized typically as having viscosity indices of 80 or greater, preferably 100 or greater, and more preferably 120 or greater. Additionally, in certain particular instances, viscosity index of these base stocks may be preferably 130 or greater, more preferably 135 or greater, and even more preferably 140 or greater. For example, GTL base stocks and base oils that derived from GTL materials preferably F-T materials especially F-T wax generally have a viscosity index of 130 or greater. References herein to viscosity index refer to ASTM method D2270.

In addition, the GTL base stocks and base oils are typically highly paraffinic (>90% saturates), and may contain mixtures of monocycloparaffins and multicycloparaffins in combination with non-cyclic isoparaffins. The ratio of the naphthenic (i.e., cycloparaffin) content in such combinations varies with the catalyst and temperature used. Further, GTL base stocks and base oils typically have very low sulfur and nitrogen content, generally containing less than about 10 ppm, and more typically less than about 5 ppm of each of these elements. The sulfur and nitrogen content of GTL base stock and base oil obtained by the hydroisomerization/isodewaxing of F-T material, especially F-T wax is essentially nil.

Useful compositions of GTL base stocks and base oils, hydro-isomerized or isodewaxed F-T material derived base stocks and base oils, and wax-derived hydroisomerized/isodewaxed base stocks and base oils, such as wax isomerates/isodewates, are recited in U.S. Pat. Nos. 6,080,301 and 6,165,949 for example.

In a preferred embodiment the GTL material is a material derived from the F-T synthesis process. In a F-T synthesis process, a synthesis gas comprising a mixture of H₂ and CO is catalytically converted into hydrocarbons and preferably liquid hydrocarbons. The mole ratio of the hydrogen to the carbon monoxide may broadly range from about 0.5 to 4, but which is more typically within the range of from about 0.7 to 2.75 and preferably from about 0.7 to 2.5. As is well known, F-T synthesis processes include processes in which the catalyst is in the form of a fixed bed, a fluidized bed or as a slurry of catalyst particles in a hydrocarbon slurry liquid. The stoichiometric mole ratio for a F-T synthesis reaction is 2.0, but there are many reasons for using other than a stoichiometric ratio as those skilled in the art know. In a cobalt slurry hydrocarbon synthesis process the feed mole ratio of the H₂ to CO is typically about 2.1/1. The synthesis gas comprising a mixture of H₂ and CO is bubbled up into the bottom of the slurry and reacts in the presence of the particulate F-T synthesis catalyst in the slurry liquid at conditions effective to form hydrocarbons, a portion of which are liquid at the reaction conditions and which comprise the hydrocarbon slurry liquid. The synthesized hydrocarbon liquid is separated from the catalyst particles as filtrate by means such as filtration, although other separation means such as centrifugation can be used. Some of the synthesized hydrocarbons pass out the top of the hydrocarbon synthesis reactor as vapor, along with unreacted synthesis gas and other gaseous reaction products. Some of these overhead hydrocarbon vapors are typically condensed to liquid and combined with the hydrocarbon liquid filtrate. Thus, the initial boiling point of the filtrate may vary depending on whether or not some of the condensed hydrocarbon vapors have been combined with it. Slurry hydrocarbon synthesis process conditions vary somewhat depending on the catalyst and desired products. Typical conditions effective to form hydrocarbons comprising mostly C₅₊ paraffins, (e.g., C₅₊-C₂₀₀) and preferably C₁₀₊ paraffins, in a slurry hydrocarbon synthesis process employing a catalyst comprising a supported cobalt component include, for example, temperatures, pressures and hourly gas space velocities in the range of from about 320-850° F., 80-600 psi and 100-40,000 V/hr/V, expressed as standard volumes of the gaseous CO and H₂ mixture (0° C., 1 atm) per hour per volume of catalyst, respectively. It is preferred that the hydrocarbon synthesis reaction be conducted under conditions in which limited or no water gas shift reaction occurs and more preferably with no water gas shift reaction occurring during the hydrocarbon synthesis. It is also preferred to conduct the reaction under conditions to achieve an alpha of at least 0.85, preferably at least 0.9 and more preferably at least 0.92, so as to synthesize more of the more desirable higher molecular weight hydrocarbons. This has been achieved in a slurry process using a catalyst containing a catalytic cobalt component. Those skilled in the art know that by alpha is meant the Schultz-Flory kinetic alpha. While suitable F-T reaction types of catalyst comprise, for example, one or more Group VIII catalytic metals such as Fe, Ni, Co, Ru and Re, it is preferred that the catalyst comprise a cobalt catalytic component. In one embodiment the catalyst comprises catalytically effective amounts of Co and one or more of Re, Ru, Fe, Ni, Th, Zr, Hf, U, Mg and La on a suitable inorganic support material, preferably one which comprises one or more refractory metal oxides. Preferred supports for Co containing catalysts comprise titania, particularly. Useful catalysts and their preparation are known and illustrative, but nonlimiting examples may be found, for example, in U.S. Pat. Nos. 4,568,663; 4,663,305; 4,542,122; 4,621,072 and 5,545,674.

Preferably, the F-T waxy material is one having an initial boiling point in the range of from about 650° F. to 700° F. and preferably boils continuously up to an end point of at least 1050° F.

The waxy material is hydroprocessed to produce a GTL base oil. Such hydroprocessing techniques are well known in the art. In this regard see, for example, other isomerization catalysts and processes for hydrocracking/hydroisomerized/isodewaxing GTL materials and/or waxy materials to base stock or base oil are described, for example, in U.S. Pat. Nos. 2,817,693; 4,900,407; 4,937,399; 4,975,177; 4,921,594; 5,059,299; 5,200,382; 5,516,740; 5,182,248; 5,290,426; 5,580,442; 5,976,351; 5,935,417; 5,885,438; 5,965,475; 6,190,532; 6,375,830; 6,332,974; 6,103,099; 6,025,305; 6,080,301; 6,096,940; 6,620,312; 6,676,827; 6,383,366; 6,475,960; 5,059,299; 5,977,425; 5,935,416; 4,923,588; 5,158,671; and 4,897,178; EP 0324528 (B1), EP 0532116 (B1), EP 0532118 (B1), EP 0537815 (B1), EP 0583836 (B2), EP 0666894 (B2), EP 0668342 (B1), EP 0776959 (A3), WO 97/031693 (Al), WO 02/064710 (A2), WO 02/064711 (A1), WO 02/070627 (A2), WO 02/070629 (A1), WO 03/033320 (A1) as well as in British Patents 1,429,494; 1,350,257; 1,440,230; 1,390,359; WO 99/45085 and WO 99/20720. Particularly favorable processes are described in European Patent Applications 464546 and 464547. Processes using F-T wax feeds are described in U.S. Pat. Nos. 4,594,172; 4,943,672; 6,046,940; 6,475,960; 6,103,099; 6,332,974; and 6,375,830.

The GTL base oil comprises a major amount of the total composition of the invention. Typically, it will comprise greater than about 55 volume percent of the composition and preferably greater than about 60 volume percent of the composition.

In addition to comprising a major amount of a GTL base oil, the lubricating composition of the invention includes two-stroke engine performance additives known in the art and selected from the group consisting of extreme pressure additives, anti-foaming agents, pour point depressants, rust inhibitors, antioxidants, detergents, dispersants and hydrocarbon solvents. Such additives are used in effective amounts, typically in the range of about 0.1 weight percent to about 15.0 weight percent based on the total weight of the composition.

When mixed in an effective amount with gasoline and fed to an operating two-stroke engine, the lubricating composition results in engine emissions having reduced observable smoke. Indeed, use of the compositions of the invention will provide engine emissions having a smoke index greater than about 75 as measured by the JASO M 342-92 test. This test was established by the Society of Automotive Engineers of Japan (JSAE) for two-stroke engines and published by the Japan Automotive Standards Organization (JASO).

The examples which follow serve to illustrate the invention.

EXAMPLES

Two oils were evaluated for smoke generating properties in accordance with the JASO M 342-92 test. In this test the result is expressed as a Smoke Index and is referenced against a standard two-stroke oil with a smoke index of 100. The higher the smoke index, the greater is the reduction in smoke emissions. The GTL base oil used had a VI of 142, a KV 169 40° C. of 23.99 and @100° C. of 5.05 and a pour point of −24° C.

The composition of the test oils is given in Table 1 below. TABLE 1 Comparative 1 Example 1 Components Volume Percent Volume Percent GTL Base Stock 0.0 62.6 150 N Base Stock 45.6 0.0 300 N Base Stock 17.0 0.0 Lubrizol 682F Additive Package 5.0 5.0 Acryloid 54 70 0.4 0.4 Varsol 3189 Solvent 20.0 20.0

The kinematic viscosity of the compositions are given in Table 2. TABLE 2 Comparative Example 1 KV @ 40° C., cSt 25.18 30.44 KV @ 100° C., cSt 5.95 5.78

The smoke index for the comparative conventional composition was found to be 65, while that for the Example composition was found to be significantly better at 78. 

1. A two-stroke gasoline engine oil comprising: a major amount of a GTL base oil; and an effective amount of at least one additive selected from the group consisting of extreme pressure additives, anti-foaming agents, pour point depressants, rust inhibitors, antioxidants, detergents, dispersants and hydrocarbon solvents.
 2. The oil of claim 1 wherein the GTL base oil has a kinematic viscosity at 100° C. from about 2 cSt to about 50 cSt and a VI greater than
 80. 3. The oil of claim 2 wherein the GTL base oil is derived from a F-T wax.
 4. The oil of claim 3 wherein the GTL base oil contains mixtures of cycloparaffins.
 5. The oil of claim 3 wherein said oil has a smoke index greater than about
 75. 6. A method for reducing the observable smoke emitted from a two-stroke gasoline engine comprising: providing the engine under conditions of use with a mixture of gasoline and a lubricating composition wherein the lubricating composition comprises a major amount of a GTL lubricating base oil.
 7. The method of claim 6 wherein the GTL base oil has a kinematic viscosity at 100° C. from about 2 cSt to about 50 cSt and a VI greater than about
 80. 8. The method of claim 6 wherein the GTL base oil is derived from a F-T wax.
 9. In a two-stroke internal combustion engine comprising lubricant, the improvement wherein the lubricant comprises: a major amount of a GTL base oil; an effective amount of at least one additive selected from the group consisting of extreme pressure additives, anti-foaming agents, pour point depressants, rust inhibitors, antioxidants, detergents, dispersants and hydrocarbon solvents; and wherein the smoke index resulting from lubricant is greater than about
 75. 10. The improvement of claim 9 wherein the GTL base oil has a kinematic viscosity at 100° C. from about 2 cSt to about 50 cSt and a VI greater than about
 80. 11. The improvement of claim 10 wherein the GTL base oil is derived from a F-T wax. 